Include `nodes.h` in `nodes_shared.h` to help editing tools.

This include does not change anything to compilation, but it helps
editing tools (e.g. YouCompleteMe) to show proper error messages when
editing that file.

Test: mma -j40

Change-Id: I5ebd03040cfc90daa41faf85f273a86525207f19
diff --git a/compiler/optimizing/nodes_shared.h b/compiler/optimizing/nodes_shared.h
index 8bd8667..ff9b5e9 100644
--- a/compiler/optimizing/nodes_shared.h
+++ b/compiler/optimizing/nodes_shared.h
@@ -17,6 +17,11 @@
 #ifndef ART_COMPILER_OPTIMIZING_NODES_SHARED_H_
 #define ART_COMPILER_OPTIMIZING_NODES_SHARED_H_
 
+// This `#include` should never be used by compilation, as this file (`nodes_shared.h`) is included
+// in `nodes.h`. However it helps editing tools (e.g. YouCompleteMe) by giving them better context
+// (defining `HInstruction` and co).
+#include "nodes.h"
+
 namespace art {
 
 class HMultiplyAccumulate FINAL : public HExpression<3> {